The steroid-receptor protein complex is believed to activate gene transcription by binding to unique DNA sequences within promoter sequences of certain genomes. Research in the present intramural project has uncovered a novel aspect in this activation mechanism--covalent addition to and removal of ADP-ribose from chromosomal proteins are essential control points. During the current time period we have found that certain ADP-ribosylated chromosomal proteins are removed from chromatin by mild digestion with nuclease demonstrating that these modified proteins are not randomly distributed throughout chromatin but rather are probably associated with actively transcribed genes. Glucocorticoids are more effective genomic activators and even glucocorticoid antagonists can function as agonists in cells devoid of ADP-ribosylated proteins suggesting that ADP-ribosylated chromosomal proteins may hinder receptor binding to chromatin and activation of genomes. Nicotinamide and its derivaties also activate a glucocorticoid promoter replicating as an episome. The carcinogen N-methyl-N'-nitro-N-nitrosoguanidine rapidly depletes NAD levels in cells by activation of (ADP-ribose)n synthetase and not by causing extrusion of NAD into the culture media. Endogenous ADP-ribosylation of some but not all chromosomal proteins is increased by MNNG treatment.